A 1992 law called for all records surrounding the assassination to be made public, but the National Archives says it needs more time to review the files to ensure their release wouldn't cause harm.
In one memo written just after President Kennedy's suspected assassin Lee Harvey Oswald was murdered by Jack Ruby, FBI Director J. Edgar Hoover called it "inexcusable" he wasn't protected.
The vast majority of what's being held secret is at the request of the FBI and CIA. The White House is establishing a six-month review process for those remaining records.